Why is my Ruby On Rails database query so slow?

Question

The following code always uses more then ten seconds. I have upgraded the server, but it doesn't help. I know I have some database design problems, but I can't modify that.

I am showing all the prices from differents locations of products of a category also in different time range, because the prices change every 15 days in each location.

controller

def prods_x_cat
 # This will load all the products of a category
 @products =  Product.prods_x_cat(params[:id],:include => :raw_datas)
 @cortes = RawData.cortes
  respond_to do |format|
    format.js { render :layout=>false}
  end
end

prods_x_cat.js.erb

 var jqxhr1 = $.ajax($("#loading_overlay .loading_message, #loading_overlay").fadeIn());
 $('#datos').html("<%= escape_javascript render :partial=>'/shared/prods_x_cat'%>")

view

    <%@cortes.each do |c|%>
  <a href="#<%=c.corte%>" class="round_top"><%=c.corte%></a>
    <%end%>
    <%@cortes.each do |c|%>
     <%@fecha = c.corte_real%>
     <div id="<%=c.corte%>" class="block no_padding">
     <table class="display datatable">
    <thead>
    <tr>
      <th>SKU</th>
            <%Company.active.order('table_field ASC').each do |c|%>
                <th><%=c.abbr%></th>
            <%end%>
      <th>Average</th>
      <th>Mode</th>
      <th>Minimum</th>
      <th>Maximum</th>
     </tr>
    </thead>
    <tbody>
    <%@products.each do |p|%>
     <tr class="gradeA">
    <td><%=p.name%></td>
    <%p.raw_datas.where("product_id='#{p.id}' and corte_real='#{@fecha}'").each do |prd|%>
      <td><%=prd.location1.to_f.round(2)%></td>
      <td><%=prd.location2.to_f.round(2)%></td>
      <td><%=prd.location3.to_f.round(2)%></td>
      <td><%=prd.location4.to_f.round(2)%></td>
      <td><%=prd.location5.to_f.round(2)%></td>
      <td><%=prd.location6.to_f.round(2)%></td>
      <td><%=prd.location7.to_f.round(2)%></td>
      <td><%=prd.location8.to_f.round(2)%></td>
      <td><%=prd.promedio.to_f.round(2)%></td>
      <td><%=prd.moda%></td>
      <td><%=prd.minimo.to_f.round(2)%></td>
      <td><%=prd.maximo.to_f.round(2)%></td>
     <%end%>
     </tr>
    <%end%>
    </tbody>
    </table>
   </div>
   <%end%>
   </div> 

Answer 1

This kind of question is pretty much impossible to answer without seeing all the code involved. Instead I can help you try to figure out where the problem is.

There are good tools for finding where your performance problems are (eg ruby-prof) but if you want a quick primitive way to find where your issue is, just use Time.now . For example, you could change your controller action to be:

def prods_x_cat
 # This will load all the products of a category
 a1 = Time.now
 @products =  Product.prods_x_cat(params[:id],:include => :raw_datas)
 b1 = Time.now
 p "Time for finding products: #{b1 - a1}"
 a2 = Time.now
 @cortes = RawData.cortes
 b2 = Time.now
 p "Time for finding cortes: #{b2 - a2}"
 respond_to do |format|
   format.js { render :layout=>false}
 end
end

If the printouts suggest that the time is taken up elsewhere, start doing something similar in your template. Focus on the database calls.